Non-contact printers which utilize electrostatically charged and non-charged droplets are generally known as evidenced by U.S. Pat. Nos. 3,373,437 to Sweet et al; 3,560,988 to Krick; 3,579,721 to Kaltenbach; and 3,596,275 to Sweet. Typically, fluid filaments of e.g. ink, dye, etc. are issued through respective orifices of an orifice plate. An array of individually controllable electrostatic charging electrodes is disposed downstream of the orifice plate along the so-called "droplet formation zone." In accordance with known principles of electrostatic induction, the fluid filament is caused to assume an electrical potential opposite in polarity and related in magnitude to the electrical potential of its respective charging electrode. When a droplet of fluid is separated from the filament, this induced electrostatic charge is trapped on and in the droplet. Thus, subsequent passage of the charged droplet through an electrostatic field will cause the droplet to be deflected away from a normal droplet path towards a droplet catching structure. Uncharged droplets, on the other hand, proceed along the normal droplet path and are eventually deposited upon a receiving substrate.
Prior proposals for providing "wire-like" electrode structures exist in the art. For example, U.S. Pat. No. 4,419,674 to Bahl et al discloses the use of an insulating substrate having notches cut into opposing end surfaces thereof, the notches at one end of the substrate being typically spaced farther apart than those at the other end so as to facilitate electrical connections. A conductive filament or wire is then wrapped around the substrate from one notch/surface to the next, the wires being subsequently severed at the connector end so as to form separate electrical circuits. The wire segments wrapped around the electrode end of the substrate are fixed in place (e.g. with epoxy or the like) and then lapped or otherwise machined so as to present flat coplanar individual charging electrode surfaces along the outer edge of the assembled structure.
Other proposals in the art exist relating to the use of woven fabrics consisting solely of conductive fibers as the constituent element in various electrode structures as evidenced by U.S. Pat. Nos. 3,955,203 to Chocholaty; 4,084,164 to Alt et al; and 4,374,387 to Iyoda et al.
The electrode of the present invention is preferably utilized as a charge electrode in a fluid jet printing apparatus whereby selected fluid droplets in a plurality of fluid droplet streams are selectively charged by means of an electrostatic charge field generated by suitable control circuitry. A woven fabric-like structure comprises an essential feature of the present novel electrode. The fabric-like structure includes a plurality of substantially parallel, but spaced apart, electrically-conductive warp fibers and a second plurality of weft fibers disposed substantially transverse relative to the warp fibers. The weft fibers are preferably provided with means to mutually electrically insulate the electrically-conductive warp fibers one from another and to maintain the warp fibers in spaced, substantially parallel alignment. The woven fabric structure is then wrapped around or otherwise attached to a substrate support so as to establish, at a forward end thereof, an area which is positionable adjacent to the fluid droplet streams. The substrate, although insulated from the electrode wires, is preferably a grounded conductor in close proximity thereto so as to provide a wire-to-ground capacitance which minimizes the "cross-talk" otherwise possible due to wire-to-wire capacitance.
Upon the application of high voltage to the electrically-conductive warp fibers, an electrostatic field will be established along the area at the forward end of the substrate support so as to generate an electrostatic field through which the fluid droplet streams pass. When utilized as a charge electrode, the present invention thus enables selected ones of the fluid droplets to be electrostatically charged.
While the present invention finds particular utility as a charge electrode in a fluid jet printing apparatus, those in this art may recognize its usefulness as an electrode in other applications. Thus, further aspects and advantages of the present invention will become more clear after careful consideration is given to the detailed description of the presently preferred exemplary embodiments thereof which follows.